Securities (Securities in a Continuous Unrealized Loss Position) (Details) $ in Thousands	Mar. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	46	31
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 320,485	$ 199,567
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (6,612)	$ (1,416)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	40	40
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 379,988	$ 395,580
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (18,813)	$ (12,119)
Number of securities in a continuous unrealized loss position total | security	86	71
Fair value of securities in a continuous unrealized loss position total	$ 700,473	$ 595,147
Unrealized losses of securities in a continuous unrealized loss position total	$ (25,425)	$ (13,535)
Obligations of U.S. government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	8	8
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 68,706	$ 69,681
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (1,787)	$ (798)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	8	8
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 86,901	$ 87,923
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (4,099)	$ (3,077)
Number of securities in a continuous unrealized loss position total | security	16	16
Fair value of securities in a continuous unrealized loss position total	$ 155,607	$ 157,604
Unrealized losses of securities in a continuous unrealized loss position total	$ (5,886)	$ (3,875)
Mortgage-backed securities issued by U.S. government-sponsored agencies and U.S. government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	32	20
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 249,667	$ 128,965
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (4,807)	$ (613)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	22	22
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 265,077	$ 279,693
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (12,828)	$ (7,120)
Number of securities in a continuous unrealized loss position total | security	54	42
Fair value of securities in a continuous unrealized loss position total	$ 514,744	$ 408,658
Unrealized losses of securities in a continuous unrealized loss position total	$ (17,635)	$ (7,733)
Individual name issuer trust preferred debt securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	0	0
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 0	$ 0
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ 0	$ 0
Number of securities in a continuous unrealized loss position for 12 months or longer | security	7	7
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 17,096	$ 16,984
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (1,016)	$ (1,122)
Number of securities in a continuous unrealized loss position total | security	7	7
Fair value of securities in a continuous unrealized loss position total	$ 17,096	$ 16,984
Unrealized losses of securities in a continuous unrealized loss position total	$ (1,016)	$ (1,122)
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	6	3
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 2,112	$ 921
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (18)	$ (5)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	3	3
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 10,914	$ 10,980
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (870)	$ (800)
Number of securities in a continuous unrealized loss position total | security	9	6
Fair value of securities in a continuous unrealized loss position total	$ 13,026	$ 11,901
Unrealized losses of securities in a continuous unrealized loss position total	$ (888)	$ (805)